A popular feature of folding knives is a locking mechanism that prevents the blade of the knife from closing unintentionally and unexpectedly. Two popular types of such locks include the lock back and the liner lock. The lock back structure provides a spring-biased lever mounted along one side of a handle. The lever has a front hook or tooth that engages in a notch in the tang portion of the blade, adjacent to the point of pivotal attachment of the blade to the handle. The liner lock structure provides a thin liner of sheet metal that springs into place behind a flat portion of the tang of the blade, thereby preventing closure until the liner is manually moved out of the way of the blade.
Despite the popularity of these structures, there still are instances of lock failure or, more often, inadvertent releasing of the lock. Another problem is a lock which requires or encourages the user to have a finger or part of his or her hand in the path of a closing blade when the release mechanism is actuated, because of the arrangement of the parts and the actions necessary for releasing the lock.